Test Sequence

In many instances, emissions systems must fail diagnostic tests more than once before PCM illuminates MIL. These tests are know as "2 trip monitors". Other tests that turn MIL lamp on after a single failure are known as "one trip monitors". A trip is defined as "start vehicle and operate it to meet criteria necessary to run given monitor".

Many of diagnostic tests must be performed under certain operating conditions. However, there are times when tests cannot be run because another test is in progress (conflict), another test has failed (pending) or Task Manager has set a fault that may cause a failure of test (suspend).

• Pending -  Under some situations Task Manager will not run a monitor if MIL is illuminated and a fault is stored from another monitor. In these situations, Task Manager postpones monitors pending resolution of original fault. The Task Manager does not run test until problem is remedied.

  For example, when MIL is illuminated for an Oxygen Sensor fault, Task Manager does not run Catalyst Monitor until Oxygen Sensor fault is remedied. Since Catalyst Monitor is based on signals from Oxygen Sensor, running test would produce inaccurate results.

• Conflict -  There are situations when Task Manager does not run a test if another monitor is in progress. In these situations, effects of another monitor running could result in an erroneous failure. If this conflict is present, monitor is not run until conflicting condition passes. Most likely monitor will run later after conflicting monitor has passed.

  For example, if Fuel System Monitor is in progress, Task Manager does not run Catalyst Monitor. Since both tests monitor changes in air/fuel ratio and adaptive fuel compensation, monitors will conflict with each other.

• Suspend -  Occasionally Task Manager may not allow a two trip fault to mature. The Task Manager will suspend maturing of a fault if a condition exists that may induce an erroneous failure. This prevents illuminating MIL for wrong fault and allows more precise diagnosis.

  For example, if PCM is storing a one trip fault for Oxygen Sensor and catalyst monitor, Task Manager may still run Catalyst Monitor, but will suspend results until Oxygen Sensor Monitor either passes or fails. At that point Task Manager can determine if catalyst system is actually failing or if an Oxygen Sensor is failing.